The field of the invention is cross flow filtration used to remove oily residues from aqueous waste streams.
Aqueous waste streams produced by petroleum producing and processing operations often contain oily residues that must be removed before discharge. Conventional methods for removing the residues often require the use of large settling tanks or bulky equipment which are impractical in locations where space is limited, as, for example, on an off-shore oil platform. Filtration devices, although showing promise have been found to quickly clog under field operating conditions and require frequent maintenance to remain operable.
The use of cross-flow filtration in which the feed stream flows under pressure parallel to the filter surface producing two streams out of the filter module has been described by R. H. Bhave et al. in "Removal Of Oily Contaminants In Wastewater With Microporous Alumina Membranes" (AlChE Symposium Series, No. 261, Vol. 84, pages 19-27). Cross-flow filtration due to the continual sweeping of the membrane surface by the feed stream usually will demonstrate less fouling of the membrane than flow through filtration and, as such, is able to operate for a longer period of time before cleaning is required.
Field tests conducted using ceramic membranes in cross-flow filtration systems to remove oil and grease from aqueous waste streams produced on off-shore platforms have found that although initially the membrane separation process reduced the total organics to low levels, fouling of the membrane remains a problem in the presence of certain organics. Over long duration runs the filtration rate decreases significantly, and the membranes have been found to be difficult to clean.